What you are talking about is a media server or a media player. Not only do they make them, but they come in all types of different shapes, sizes, and colors.
The hard part is really figuring out EXACTLY what it is that you are trying to accomplish.
Video files have about 2,000 different video encoders/decoders available (codecs) and almost no player is capable of actually doing everything that someone wants. Popcorn Hour has some nice product, as does the aforementioned Dune. I'm prebably going with a Dune product for the horsepower it delivers. But, I will be networking it to a Windows Home Server and several TB of Blu-ray Disc rips (original ISO format).
I've taken my DVD collection to MP4 format for my AppleTV, but the quality is nothing like the original DVD, so I'm moving away from that and will probably stick with original media rips.
As to just plugging a hard drive into your receiver...
You would need a receiver which is capable of decoding the video files in all 2,000+ flavors that they may be in from that hard drive.
So, the media player is that interface which will do it for you and give you a traditional HDMI, component video, and/or composite video output with associated audio.
The PS3 does it. The X-Box 360 does it.
There are a number of cheaper players which can do it as well, notably the Western Digital TV (WDTV) allows for a networked or USB hard drive right to it and will play back a number of different file formats and is around $100.00. Not to bad!